Enriched high conductivity geothermal fill and method for installation

ABSTRACT

A geothermal fill material composed of one or more high heat conductivity materials alone or in combination to produce a fill that can be used to cover and encapsulate geothermal ground coils to improve heat transfer between the ground and the fluid inside the coils and to improve the rate of heat recovery of the fill in contact and in the vicinity of the coils. These materials can be in the form of particulates, rods or wire mesh and in any combination. Further enhancements are to cover this high conductivity material with low conductivity materials near the surface of the ground or to install the coils in a ground coil field below a structure in order to reduce ground heat loss to the atmosphere in the winter and to reduce heat gain from the atmosphere in the summer.

REFERENCES CITED [REFERENCES BY]

U.S. Patent Documents 5,477,914 December 1995 Rawlings 165/45 5,533,355 July 1996 Rawlings 165/45 5,738,164 April 1998 Hilderbrand 165/45 6,251,179 June 2001 Allan 106/719

FIELD OF INVENTION

The present invention relates to heat recovery systems and methods, and more particularly pertains to a system and method whereby the fill used to cover and surround geothermal coils is used in combination with high heat conductivity materials to improve heat transfer and heat recovery from the ground.

BACKGROUND OF THE INVENTION

Several prior art patents have utilized the earth as a source of heat and as a heat sink. Commercial geothermal energy systems are available and have been in use for several years. These systems normally utilize a water feed heat pump for both heating and cooling. The circulating fluid that feeds the heat pump flows through tubes that are buried deep in the ground and the circulating fluid uses the ground surrounding the tubes as both a heat source and a heat sink depending on whether it is being used for heating or cooling. In northern climates the primary use for these systems would be for heating buildings, with air conditioning as a secondary use.

Geothermal systems are usually installed by drilling vertical holes into the ground or digging open excavations in the ground and installing polymer or other types of coils vertically in the drill holes or horizontally in the excavations. The horizontal coils are then covered with the natural ground material removed from the excavations. These systems are dependant on using the natural ground formations as a heat source when heating is required and as a heat sink when cooling is required and depend on the natural heat transfer coefficient from the ground and the natural heat flux in the ground for temperature recovery of the ground in the vicinity of the coils which is dependant on the heat conductivity of the ground which can be as low as less than 1.0 W/m.K.

U.S. Pat. No. 5,738,164 (Hilderbrand) describes such a system using bore wells in the ground. U.S. Pat. No. 5,533,355 (Rawlings) describes a ground source heat system. These and similar patents all depend on the normally occurring temperatures and conductivity of the natural ground formations at the location where the geothermal system coils are installed. U.S. Pat. No. 6,251,179 (Allan) describes a grout that is pumped into the vertical bore holes after the installation of the ground coils in order to improve the contact and heat transfer from the ground to the fluid in the ground coils.

All of the referenced patents suffer from the shortcoming that they do not address the most common limiting factor in geothermal systems during the heating season, which is the inability of the ground, in contact and in the immediate vicinity of the ground coils, to readily recover the heat that is transferred to the fluid in the coils. This causes the ground temperature in the vicinity of the coils to be lowered, which in turn reduces the capacity and the efficiency of the system. The referenced patents also do not address the most common limiting factor during the cooling season, which is the inability of the ground in contact and in the vicinity of the coils to dissipate the heat transferred from the liquid in the coils. These limiting factors are directly related to the heat conductivity of the ground.

During the coldest periods of the year, the heat load obviously increases and the heat removal requirement from the ground in contact with the geothermal coils also increases but the natural heat recovery by the ground surrounding the coil is too slow to maintain the normal ground temperature which becomes the limiting factor for the entire geothermal system. This phenomenon lowers the ground temperature near the coil and in turn lowers the temperature of the circulating fluid which reduces the heating capacity of the geothermal system. During these periods, the heating system of the building normally incorporates electric heating coils to make up for the shortfall of the geothermal system. The energy costs increase because of the auxiliary electric heating requirements. This greatly reduces the return on investment used to justify the geothermal system.

Applying the teachings of our invention leads to a substantial increase in the heat conductivity of the fill in contact with the ground coils as well as for the entire ground coil field material used to fill the excavation after the installation of the coils. Higher conductivity of the fill results in rapid heat recovery in the heating season and rapid heat dissipation during the cooling season of the fill in the vicinity of the coils. This maintains the peak design capacities of the system during the coldest winter months and hottest summer months.

Theoretically the deeper the bore holes or the deeper the excavation the warmer the ground temperature, however the drilling costs or the excavation costs to install the ground coils will increase with the depth. An enhancement of our invention would be to reduce excavation costs at new construction sites by installing the ground coils, and high heat conductivity fill, just below excavations that are required for below ground level floors, basements or any other independent reason related to the construction site. By taking advantage of these required existing excavation sites, the majority of the cost of a separate dedicated excavation for the installation of the geothermal ground coils can be avoided. Extra advantages of installing the ground coils below a structure, are that in winter the concrete floor of the structure covers the ground coil field which eliminates any loss of ground heat to the cold atmosphere and also provides a relatively warm surface in contact with the top of the ground coil field. In summer the floor prevents the hot atmosphere from warming the top of the ground coil field and also acts as an additional heat sink to dissipate heat transferred by the fluid in the ground coils. These additional advantages can be achieved even if the structure is on a slab without a basement. Without any structure at all, the loss of heat to the atmosphere in the winter and the gain of heat from the atmosphere in the summer can also be minimized by adding a layer of low conductivity material above the high conductivity geothermal ground coil field starting preferably but not limited to, from the frost line up to ground level.

SUMMARY OF THE INVENTION

This invention describes a process whereby one or more materials that have high heat conductivity characteristics with values of 1.5 W/m.K. or higher are used alone or in combination with other fill materials to produce an enriched high heat conductivity fill that can be used to cover and encapsulate ground coils which are an integral part of geothermal energy systems. These high heat conductivity materials, with values of 1.5 W/m.K or higher, can be in the form of minerals such as bentonite or iron ore and other ores, metals such as iron and steel scrap or rods and mesh similar to those used to reinforce concrete or crushed aluminum cans from recycle centers, ceramics such as Corningware® and other cooking ware scraps, glass scraps such as Pyrex® and similar cooking ware, polymers with high heat conductivity fillers and other compositions. These high heat conductivity materials, with values of 1.5 W/m.K or higher, should also have the proper chemical and physical characteristics to make them suitable for ground fill and should not contain any toxic, hazardous or environmentally undesirable materials.

Loss of ground heat to the cold atmosphere in the winter and gain of ground heat by the hot atmosphere in the summer is reduced by the use of a layer of low heat conductivity (1.0 W/m.K or lower) material above the geothermal ground coil field or by installing the coils below a structure. Installation costs are reduced by taking advantage of excavations already made for below ground floors, basements or any other independent reason instead of requiring a completely separate and dedicated excavation for the installation of the geothermal ground coils.

Using the teachings of our invention, the heat transfer of the ground in contact with and in the vicinity of the ground coils is greatly improved and the heat recovery is greatly increased, thereby minimizing or completely eliminating the need for supplemental electric heating, improving efficiency and the capacity of the system and reducing capital and operating cost for both heating and cooling.

DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating the heat conductivity of various fill materials and the effect of moisture.

FIG. 2 is a schematic cross section of the preferred embodiment of the invention where the coils are installed below a structure.

FIG. 3 is a schematic cross section of an embodiment of the invention where the coils are not installed below a structure.

FIG. 4 is a top view of FIG. 3 with the fill removed to show detail.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THIS INVENTION

Materials that are tested to have higher heat conductivity properties than natural ground formation, which can be lower than 1.0 W/m.K, and that have the proper chemical, physical and drainage characteristics to make them suitable for ground fill are used in combination with each other and natural good conductivity ground fill to cover and encapsulate geothermal ground coils installed in excavations. Improving the conductivity of the fill that covers and encapsulates the coils to above 1.5 w/m.K, will improve the heat transfer rate from the bulk of the ground to the fluid inside the coils, and more importantly, increase the rate of heat recovery of the fill in the vicinity of the ground coils. This minimizes or eliminates the need for supplemental electric heating coils, improving the overall efficiency of the geothermal heating system.

In the summer when cooling is required, the higher conductivity fill improves the rate of heat removal from the fill around the ground coils therefore providing a better heat sink during the cooling cycle and improving energy efficiency.

This invention comprises of the use of materials with good heat conductivity of greater than 1.5 W/m.K, and proper chemical and physical properties to improve the rate of heat transfer and heat recovery of the fill encapsulating geothermal ground coils. These materials must be clean and cannot contain any toxic substances that could be considered as a source of pollution or in any way have an adverse affect on the environment.

Types of these materials, but not limited to, are as follows:

-   -   1. Natural minerals preferably with high metallic content such         as bentonite, iron pyrites, metal ores and certain types of         slag.     -   2. Clean metals or byproducts from metallurgical processes,         preferably corrosion resistant and can be in the form of         particulates, rods or mesh such as iron or steel used to         reinforce concrete and crushed aluminum cans from recycle         centers.     -   3. High heat conductivity (greater than 1.5 W/m.K) ceramics         preferably from production scrap of ceramic cookware such as         Corningwear® and similar products.     -   4. High heat conductivity (greater than 1.5 W/m.K) glass         preferably from the production scrap of glass cookware such as         Pyrex® and similar cooking products.     -   5. High heat conductivity (greater than 1.5 W/m.K) polymers         preferably from composites that contain high heat conductivity         (greater than 1.5 W/m.K) fillers or metals.     -   6. Any other material that has higher heat conductivity (greater         than 1.5 W/m.K) than natural ground formations.

The selected materials can be processed by normal rock crushing, sizing, mixing and other types of equipment to form particulates and mixed with natural high heat conductivity fill material. The ratio of the materials in the mix will vary depending on the availability of the components and the economics including transportation and processing cost.

In the preferred embodiment of this invention referring to FIG. 2, scraps of clean, high heat conductivity particulates 1 from ceramic cookware factories, metallurgical factories, mineral processing plants or any other high conductivity material plant are crushed, sized and blended with natural high conductivity sand and gravel. This high conductivity fill 2 is then used to form a shallow bed at the bottom of an excavation 3 that was dug in a natural ground formation 4 for the basement 5 of a structure 6 and then deepened to accommodate the installation of the ground coils 7 and the high conductivity fill 2.

A bottom metal mesh 8 similar to those used to reinforce concrete is placed on the bed, the geothermal ground coils 7 are then installed on the bottom wire mesh 8 and high conductivity grout 9 is used to bond the ground coils 7 to the bed and the bottom wire mesh 8. More high conductivity fill 2 is added to raise the level of the high conductivity fill 2 to the top of the coils 7.

A top wire mesh 10 is added above the ground coils 7 and metal rods 11 are then pushed into the bed preferably vertically but can be at any angle at frequent intervals along the length of the ground coils 7. The metal rods 11 should preferably extend from the bottom of the bed to preferably three or more feet above the ground coil 7. High conductivity grout 8 is then used to bond the coil 6 to the top mesh 10 and the rods 11. The remaining high conductivity fill 2 is added up to the level of the basement floor 12 of the structure 6. The concrete basement floor 12 is then poured over the ground coil field in the normal manner and the structure 6 is erected in a normal manner.

In cases where the geothermal ground coil fields are not installed below a structure 6, as in FIG. 3, the remaining high conductivity fill 2 is added up to about three feet below ground level 13, then low conductivity materials 14, such as clay or non-toxic, non-polluting. low density, low conductivity materials 14 can then be used for the next two feet or so. Top soil 15 can then be used on top, up to ground level 13 and can be used for a lawn or any other purpose to improve aesthetics. The installation sequence can be modified and all of the above steps are not necessary to practice the spirit of our invention.

This configuration improves the heat transfer within the ground fill because of the use of high conductivity fill 2 that is specifically selected and blended to have high heat conductivity. The heat transfer is further enhanced by the very high heat conductivity of the bottom metal mesh 8 and the top metal mesh 10 which provide horizontal heat transfer across the high conductivity fill 2 and the metal rods 11 which provide heat transfer vertically over the area of the ground coil field. This also provides a method for very rapid heat recovery of the fill 2 in the vicinity and in direct contact with the ground coils 7. This insures high circulating liquid temperatures even during the coldest months thereby reducing the necessity for supplemental electric heat and thereby increases energy efficiency and reduces cost. In the summer during the cooling season, this configuration also allows for rapid dissipation of heat away from the geothermal ground coil keeping the ground temperature in contact and in the vicinity of the coils from rising and thereby maintains high energy efficiency and improved capacity of the geothermal system. 

1. A process whereby materials with higher heat conductivity than natural ground formations, which are typically 1.1 W/m.K or lower, are selected and are used alone or in combination with natural ground materials such as sand and gravel to produce a mixture with a heat conductivity value of 1.5 W/m.K or higher and using this mixture to cover and encapsulate geothermal ground coils to improve heat transfer between the ground and the fluid inside the coils and to improve the heat recovery of the ground in contact and in the vicinity of the coils.
 2. A method of claim 1 wherein the higher heat conductivity material is metallic in nature and can be in any form such as wire mesh and rods similar to those used to reinforce concrete or in the form of particulates such as scrap metal from salvage operation or crushed aluminum cans from recycle centers.
 3. A method of claim 1 whereby the higher conductivity material consists of scrap materials from ceramic or glass cookware production such as Corningware® or Pyrex® brand products having a heat conductivity value of 1.5 W/m.K or higher.
 4. A method of claim 1 whereby the higher conductivity material is mineral in nature such as bentonite iron ore, bauxite and other metal containing minerals and ores that have a heat conductivity value of 1.5 W/m.K or higher.
 5. A method of claim 1 whereby the higher conductivity material is a polymer that has metal or other high conductivity material as fill and has a heat conductivity value of 1.5 W/m.K or higher.
 6. A process according to claim 1 where the heat loss in winter and the heat gain in summer between the ground coil field and the atmosphere is minimized by installing the ground coil field below a structure or below a layer of low heat conductivity material having a heat conductivity value of less than 1.0 W/m.K.
 7. A method of encapsulating geothermal ground coils with said high conductivity fill mixture to improve heat transfer between the ground and the fluid in the coils comprising: A. mixing particulate materials with high heat conductivity values of 1.5 W/m.K or greater to produce a high heat conductivity fill mixture of 1.5 W/m.K or greater. B. placing the high conductivity fill mixture beneath a plurality of geothermal ground coils to form a bottom layer. C. placing the high conductivity fill mixture around said ground coils to a height equal to the top of these coils. D. placing the high conductivity fill mixture over said ground coils to form a top layer.
 8. The method of claim 7 whereby metallic mesh or metallic rods, similar to those used to reinforce concrete are placed horizontally between the ground coils and the bottom and top layers of the high conductivity fill mixture and a plurality of more metal rods or metallic wire mesh are positioned vertically or at any angle to form a grid which would improve heat conductivity and heat recovery to the high conductivity fill mixture in contact and in the vicinity of the ground coils. Grout can be used to bond the ground coils to the wire mesh, rods and high conductivity fill mixture to further improve heat transfer. The elimination of any of these steps does not void the spirit of this invention. 